Fluid Physics Research Articles

Learning fluid physics from highly turbulent data using sparse physics-informed discovery of empirical relations (SPIDER)

We show how a complete mathematical model of a physical process can be learned directly from data via a hybrid approach combining three simple and general ingredients: physical assumptions of smoothness, locality and symmetry, a weak formulation of differential equations and sparse regression. To illustrate this, we extract a complete system of governing equations of fluid dynamics – the Navier–Stokes equation, the continuity equation and the boundary conditions – as well as the pressure-Poisson and energy equations, from numerical data describing a highly turbulent channel flow in three dimensions. Whether they represent known or unknown physics, relations discovered using this approach take the familiar form of partial differential equations, which are easily interpretable and readily provide information about the relative importance of different physical effects. The proposed approach offers insight into the quality of the data, serving as a useful diagnostic tool. It is also remarkably robust, yielding accurate results for very high noise levels, and should thus be well suited for analysis of experimental data.

An approach of Finding Second Derivative Finite Differences Compact Schemes

In solving problems from Computational Fluid Dynamics (CFD) and physics, huge efforts should be afforded to obtain accurate and applicable schemes for the derivatives. Based on the idea of high order polynomials, many sets of second derivative schemes are derived in this paper. These sets are grouped according to the order of the accuracy of the approximations from order three to order seven. Different types of second derivative forward, central, and backward compact with some traditinal approximations are inrtoduced at each set by the proposed method. The order of accuracy is verified of each scheme using the technique of finding the values of the coefficients for the error terms by matching both sides of the given scheme. Many schemes that are introduced in this article are applicable to some problems from science and engineering.

Mathematical analysis for flow of hybrid nanofluid over a vertical stretchable surface: Assisting and opposing flows

Research Problem: The importance of improving the temperature properties of commonly used fluids in industrial processes is being addressed in this research. Nanofluids, which are composed of extremely small particles dispersed in common liquids such as water or petrol, are the main subject of this area of study. Using a vertically stretchable surface subjected to thermal radiation, the study examines the heat transfer behavior and efficiency of nanofluids. Methodology: Nanofluids that convey heat are studied by applying the fundamental rules of fluid physics to the variables that control their motion. To measure the amount of energy transferred, a nanofluid model is used. Similarity transformations are used to convert the system’s differential equations into ordinary differential equations (ODEs). The subsequent set of nonlinear ODEs is solved using numerical methods. Utilizing graphical analysis, patterns of velocity and temperature may be seen, and their responses to changes in other parameters can be investigated. Implications: This research has important implications for our knowledge of how nanofluids act in heat transfer applications, especially when exposed to thermal radiation and working with vertically stretchy surfaces. The effects of flow direction and thermal conductivity on distributions of velocity and temperature were elucidated, among other important results. More effective heating and cooling systems may be possible as a result of these findings, which have consequences for improving heat transfer processes in industrial environments. Future Work: To better understand how nanofluids behave in heat transfer applications, future studies might investigate more complicated situations and boundary circumstances. It may be possible to optimize nanofluid formulations by studying the impact of various nanoparticle kinds and concentrations on heat transfer efficiency. Research could be more applicable to real-world industrial processes if the numerical results were experimentally validated.

Long-Range Ballistic Propagation of 80% Excitonic Fraction Polaritons in a Perovskite Metasurface at Room Temperature.

Exciton-polaritons, hybrid light-matter excitations arising from the strong coupling between excitons in semiconductors and photons in photonic nanostructures, are crucial for exploring the physics of quantum fluids of light and developing all-optical devices. Achieving room temperature propagation of polaritons with a large excitonic fraction is challenging but vital, e.g., for nonlinear light transport. We report on room temperature propagation of exciton-polaritons in a metasurface made from a subwavelength lattice of perovskite pillars. The large Rabi splitting, much greater than the optical phonon energy, decouples the lower polariton band from the phonon bath of the perovskite. These cooled polaritons, in combination with the high group velocity achieved through the metasurface design, enable long-range propagation, exceeding hundreds of micrometers even with an 80% excitonic component. Furthermore, the design of the metasurface introduces an original mechanism for unidirectional propagation through polarization control, suggesting a new avenue for the development of advanced polaritonic devices.

Cost-effective production of density-controllable monodisperse spheres for experiments in fluids

Cost-effective production method for making density-controllable monodisperse spheres is demonstrated. A sodium alginate aqueous solution containing gelatin is emulsified with canola oil. The droplet surface is covered with a calcium alginate membrane by dropping the emulsion into a calcium lactate aqueous solution. The content of the canola oil can control the sphere's density. To demonstrate the applicability of the spheres to experimental research, rheological measurements of the suspensions of the spheres were performed. The effective viscosity agrees with the theoretical formula at volume fractions of 0.7%–11.7%. The demonstration highlights that the spheres can function as neutrally buoyant solid particles in studies for the physics of fluids.

Energy performance improvement for a mixed flow pump based on advanced inlet guide vanes

The sharp decrease in the efficiency of a mixed flow pump within over-load flow rates presents a challenge for coastal drainage pumping stations. To address this issue, two different structures of advanced inlet guide vanes (AIGV), full-adjustable (FA) and half-adjustable (HA) structures, are designed to approach a better energy performance improvement strategy. Entropy production theory is applied into transient flow field to reveal their influence mechanism on the spatial distribution of energy dissipation. The primary findings are as follows: (1) AIGVs effectively solve the sharp decrease in the energy performance of mixed-flow pumps within the over-load flow rate range, broadening its efficient operation range. (2) The decrease in the axial velocity under the effect of AIGV explains the primary fluid physics of the increased efficiency. (3) The improvement in the match between the impeller inflow angle distribution and the impeller blades structure suppresses the generation and transmission of the flow separation on the pressure side, and reduce the near-wall energy dissipation. The novel HA-AIGV obtains a better flow control effect.

Surface roughness effects on transonic aircraft performance: Experimental/numerical comparisons

This work highlights the necessity of taking into account surface roughness when conducting experimental tests, and when using numerical simulations to precisely calculate the turbulent lift and drag of wind-tunnel models or real aircraft in transonic conditions. The present article is a continuation of “Turbulent drag induced by low surface roughness at transonic speeds: Experimental/numerical comparisons,” Physics of Fluids, Vol. 32, 045108 (2020) by Hue and Molton. The outcomes of this former study, which was focused on flat plate samples, are here applied to a three-dimensional aircraft configuration: the Common Research Model used as a reference in the recent international Drag Prediction Workshops. Experimental campaigns have been performed in the largest ONERA wind tunnels S1MA and S2MA involving models with average surface roughness heights Ra close to 0.5 micrometers, wingspans up to 3.5 meters, Mach and Reynolds numbers up to 0.95 and 5 million respectively. Reynolds-averaged Navier–Stokes computations based on the wind-tunnel tests have then been carried out, using the equivalent sand-grain roughness height approach as well as a Musker-type correlation to determine relevant ks values. The results of both the experimental and numerical campaigns have demonstrated that the aerodynamic coefficients of the aircraft can be significantly affected by the surface roughness, even with roughness Reynolds numbers ks+ potentially below the usual threshold values sometimes considered in engineering applications (i.e. in the order of 3.5 to 5). In particular, the surface roughness effects on lift and drag have been studied using far-field analyses to evaluate the responses of friction, viscous pressure, wave and lift-induced drag components. Finally, the numerical studies have been extended to the full-scale geometry in flight conditions in order to assess the roughness effects and potential gains in realistic aircraft operating conditions.

Reynolds-Number-Dependence of Length Scales Governing Turbulent-Flow Separation in Wall-Modeled Large Eddy Simulation

This paper proposes a Reynolds number Re scaling for the number of grid points Ncv required in wall-modeled Large Eddy Simulation (WMLES) of turbulent boundary layers (TBL) to accurately capture the regions of flow separation. Based on the various time scales in a nonequilibrium TBL, a definition of the near-wall “underequilibrium” scales is proposed (in which “equilibrium” refers to a quasi balance between the viscous and the pressure gradient terms). This length scale is shown to vary with Reynolds number as lp∼Re−2/3. A-priori analysis demonstrates that the resolution (Δ) required to reasonably predict the wall stress in several nonequilibrium flows is at least O(10)lp, irrespective of the Reynolds number and Clauser parameter. Further, a-posteriori studies (on the Boeing speed bump, Song– Eaton diffuser, Notre-Dame Ramp, and the backward-facing step) show that scaling Δ such that Δ/lp is independent of Reynolds number results in accurate predictions of separation for the same “nominal” grid across different Reynolds numbers. Finally, we suggest that near separation and reattachment points, Ncv for WMLES scale as Re4/3, which is more restrictive than the previous estimates (∼Re1) by Choi and Moin (Choi, H., and Moin, P., “Grid-Point Requirements for Large Eddy Simulation: Chapman’s Estimates Revisited,” Physics of Fluids, Vol. 24, No. 1, 2012, Paper 011702) and Yang and Griffin (Yang, X. I. A., and Griffin, K. P., “Grid-Point and Time-Step Requirements for Direct Numerical Simulation and Large-Eddy Simulation,” Physics of Fluids, Vol. 33, No. 1, 2021, Paper 015108).

Modelling and simulation on compressible multi-component gas-liquid flows with chemical reaction and phase transition effects

In this paper, mathematical models and numerical algorithm are conducted for simulating compressible two-phase multi-component reactive flows, coupling with the finite-rate-based chemistry and the instantaneous-equilibrium phase transition model. Distinctive from previous multi-component two-phase governing equations, all volume fraction transport equations, with non-conservative characteristics, of gaseous components are substituted with a thermal equilibrium assumption inside the gaseous mixture for closure. Moreover, based on the temperature polynomial (NASA-7) fitted gas properties and the stiffened gas equation of state (SG-EOS) described liquid properties, the instantaneous-equilibrium phase transition model is re-derived, and the solving strategy of the transient phase transition model is detailly provided using an algebraical approach rather than the iterative process. Having included these elements, the proposed model is validated on three canonical tests, first for pure reactive flows, second for pure two-phase flows, and third for complex compressible multi-component two-phase reactive flows with phase transition effects: hydrogen-oxygen detonation interacting with a water droplet. The cases have well demonstrated the proposed model capability and the expected fluid physics in both the multiphase and reactive flows are reproduced.

The growth-adjusted impact factors of Physics of Fluids

From Phan-Thien and Giacomin [“Growth-adjusted impact factor,” Phys. Fluids 36, 050402 (2024)], we learn that journal growth decreases impact factor (all else being held equal). In this Editorial, we apply the teachings of Phan-Thien and Giacomin [“Growth-adjusted impact factor,” Phys. Fluids 36, 050402 (2024)] to growth-adjust the impact factors of the journal Physics of Fluids. We do so for the years for which the data are available, 2001–2023. We find that, over the course of its history, the growth of Physics of Fluids often suppressed its impact factor.

The growth-adjusted CiteScores of Physics of Fluids

The growth-adjusted CiteScores of <i>Physics of Fluids</i>

Numerical calculation and characteristics of N-periodic waves of a (4+1)-dimensional Korteweg–de Vries–Calogero–Bogoyavlenskii–Schiff equation in fluid physics and plasma physics

Numerical calculation and characteristics of N-periodic waves of a (4+1)-dimensional Korteweg–de Vries–Calogero–Bogoyavlenskii–Schiff equation in fluid physics and plasma physics

Fluid Ejections in Nature.

From microscopic fungi to colossal whales, fluid ejections are universal and intricate phenomena in biology, serving vital functions such as animal excretion, venom spraying, prey hunting, spore dispersal, and plant guttation. This review delves into the complex fluid physics of ejections across various scales, exploring both muscle-powered active systems and passive mechanisms driven by gravity or osmosis. It introduces a framework using dimensionless numbers to delineate transitions from dripping to jetting and elucidate the governing forces. Highlighting the understudied area of complex fluid ejections, this review not only rationalizes the biophysics involved but also uncovers potential engineering applications in soft robotics, additive manufacturing, and drug delivery. By bridging biomechanics, the physics of living systems, and fluid dynamics, this review offers valuable insights into the diverse world of fluid ejections and paves the way for future bioinspired research across the spectrum of life.

On the analytical soliton approximations to fractional forced Korteweg–de Vries equation arising in fluids and plasmas using two novel techniques

The current investigation examines the fractional forced Korteweg–de Vries (FF-KdV) equation, a critically significant evolution equation in various nonlinear branches of science. The equation in question and other associated equations are widely acknowledged for their broad applicability and potential for simulating a wide range of nonlinear phenomena in fluid physics, plasma physics, and various scientific domains. Consequently, the main goal of this study is to use the Yang homotopy perturbation method and the Yang transform decomposition method, along with the Caputo operator for analyzing the FF-KdV equation. The derived approximations are numerically examined and discussed. Our study will show that the two suggested methods are helpful, easy to use, and essential for looking at different nonlinear models that affect complex processes.

Fluid Physics Impacting Vanadium and Other Redox Flow Batteries

The Vanadium redox flow battery (VRFB) has been intensively examined since the 1970s, with researchers looking at its electrochemical time varying electrolyte concentration time variation equations (both tank and cells, for negative and positive half cells), its thermal time variation equations, and fluid flow equations. Chemical behavior of the electrolyte ions has also been intensively examined. Our focus in this treatment is a completely new approach to understanding the physics, chemistry, and electronics of the VRFB. Here, we develop complete theoretical equations by an analytical treatment affecting the fluid flow in the VRFB as well as all other redox flow batteries, providing background derivations applicable for all of the fundamental concepts required to properly understand flow batteries. With these concepts presented, calculations are done to determine actual values for fluid velocity, strain rate, angular fluid velocity, angular momentum, rotational kinetic energy, and gravity effects on fluid velocity in a redox flow battery.

Chinese Academy of Science Journal Ranking System (2015–2023)

This work examines China's mainstream journal ranking system from the Chinese Academy of Science (CAS), including its history, recent reforms, and current operation, with a particular focus on Physics of Fluids. Using official statistics, this paper analyzes the Physics of Fluids standings in the CAS system from 2015 to 2023. During these years, Physics of Fluids experienced a significant increase in both popularity and impact. Meanwhile, the CAS system underwent substantial reforms, including the newly proposed Advanced edition, which universally boosted fluids journal academic weights in China. Most notably, the brand-new Field Normalized Citation Success Index (期刊超越指数 or FNCSI) offered a new lens through which to assess academic journal impact. Statistics reveal that Physics of Fluids is in a promising position to become the fourth Tier 1 fluids journal to enter any of CAS's Major Categories (after the Annual Review of Fluid Mechanics, Nuclear Fusion, and Plasma Sources Sciences and Technology) and the first-ever non-review-only Tier 1 fluids journal to enter the Engineering and Technology (工程技术 E&amp;T) Major Category. Finally, this paper suggests several directions for Physics of Fluids to direct future endeavors as it enjoys heightening popularity in China.

Microscopic structure of electromagnetic whistler wave damping by kinetic mechanisms in hot magnetized Vlasov plasmas

Electromagnetic transverse perturbations propagating parallel to the external magnetic field in a warm electron plasma, specifically the warm electron whistler-mode waves, are simulated in Maxwellian as well as κ distributed (with energetic tail) electrons. The Vlasov-Maxwell phase-space continuum simulations are applied to the stable and unstable (i.e. isotropic and anisotropic) VDFs. The variation of real frequency from both numerical solution of dispersion relation and simulations show limited sensitivity to electron temperature in low wave-number regime as compared to high wave number regime, however the opposite holds for the imaginary frequency or the decay rate. The analytically predicted reduction in the decay rate of the whistler-mode with increasing electron temperature is recovered by the Vlasov-Maxwell simulations. The phase-space portraits of the these cases show that after the linear damping phase of the evolution, the particles are trapped in the wave magnetic field leading to the wave amplitudes oscillating about a mean value which follow the theoretical analysis. Palmadesso and Schmidt (1971) Physics of Fluids 14, 1411.

Learning a general model of single phase flow in complex 3D porous media

Modeling effective transport properties of 3D porous media, such as permeability, at multiple scales is challenging as a result of the combined complexity of the pore structures and fluid physics—in particular, confinement effects which vary across the nanoscale to the microscale. While numerical simulation is possible, the computational cost is prohibitive for realistic domains, which are large and complex. Although machine learning (ML) models have been proposed to circumvent simulation, none so far has simultaneously accounted for heterogeneous 3D structures, fluid confinement effects, and multiple simulation resolutions. By utilizing numerous computer science techniques to improve the scalability of training, we have for the first time developed a general flow model that accounts for the pore-structure and corresponding physical phenomena at scales from Angstrom to the micrometer. Using synthetic computational domains for training, our ML model exhibits strong performance (R 2 = 0.9) when tested on extremely diverse real domains at multiple scales.

INVESTIGASI KEMAMPUAN BERNALAR ILMIAH SISWA MELALUI IMPLEMENTASI MODEL PROBLEM BASED LEARNING MATERI FISIKA FLUIDA STATIS

In this 21st century, students are required to have skills in facing the challenges of globalization, one of which is scientific reasoning skills. Scientific reasoning is the ability to think systematically and logically to solve problems. Six indicators of scientific reasoning ability include conversion reasoning, proportional reasoning, variable control, probabilistic reasoning, correlation reasoning, and hypothesis-deductive reasoning. Scientific reasoning ability can be improved by using learning models that encourage students to think at a higher level, one of which is the Problem Based Learning (PBL) model. The purpose of this research is to determine the scientific reasoning ability of students through the application of the PBL model on static fluid physics material. This type of research is descriptive quantitative and qualitative. This research was conducted in class XI MIPA 4 SMAN 3 Jember. Data collection techniques in this study using observation techniques, interviews, tests, and documentation. Data analysis techniques in this study are data collection, data reduction, data presentation, data interpretation, and conclusion drawing. The results obtained are the average score of students' reasoning ability on the six indicators of scientific reasoning in the very good category. So it is concluded that the PBL model can improve students' scientific reasoning ability in static fluid physics material.

Advancement in Generation and Application of Microfluidic Chip Technology

Microfluidics is an interdisciplinary topic of research that draws inspiration from other areas such as fluid dynamics, microelectronics, materials science, and physics. Microfluidics has made it possible to create microscale channels and chambers out of a broad variety of materials by borrowing ideas from a number of different fields. This has opened up exciting possibilities for the development of platforms of any size, shape, and geometry using a variety of approaches. One of the most significant advantages of microfluidics is its versatility in applications. Microfluidic chips can be used for a variety of purposes, such as incorporating nanoparticles, encapsulating and delivering drugs, targeting cells, analyzing cells, performing diagnostic tests, and cultivating cells. This adaptability has led to the development of several device-like systems for use in a range of settings. In this study, we explore cutting-edge novel applications for microfluidic and nanofabrication technologies. We examine current developments in the area of microfluidics and highlight their potential for usage in the medical industry. We pay special attention to digital microfluidics, a recently developed and very useful technique for illness diagnosis and monitoring. The originality of microfluidics is found in the fact that it allows for the miniaturization of complex systems and processes, paving the way for the creation of cutting-edge gadgets with wide-ranging practical applications. Microfluidics has the potential to transform various fields, including medicine, biotechnology, environmental monitoring, and more. The development of novel microfluidic platforms, coupled with advancements in digital microfluidics, promises to revolutionize the way we diagnose, treat, and monitor diseases.